Funds are requested for the purchase of a Zeiss EM10 Transmission Electron Microscope in order to meet the objectives of the following NIH projects. (1) Ovarian Nerves and Reproductive Function. This project requires the proposed instrument in studying the role of gap junctions in uterine smooth muscle during parturition, and ovarian perifollicular smooth muscle during ovulation. Also it will be used in studying the cervix in neurectomized rats with blocked parturition and the corpus luteum in pelvic neurectomized rats with blocked parturition. (2) Mechanisms of Macrophage Diversity. The proposed electron microscope is required in studying the renewal of resident macrophages and their dependence upon the influx of monocytes from the blood. Electron microscopy of marked macrophages will be used to discern if blood monocytes have migrated from the blood to replace resident macrophages lost from tissue compartments. (3) Development and Plasticity of Opioid Peptidergic Neurons. The ultrastructural aspects of this project involve the characterization of the postsynaptic target cells of opioid peptidergic neurons in the hippocampus in rats. In addition we will determine whether selective deafferentation of the hippocampus induces new opioid peptidergic synapses to form with denervated target cells. (4) Morphometry of Gonadotropes During Hyperprolactinemia. This project requires the proposed electron microscope in quantifying (morphometry) the effects of hyperprolactinemia on the pituitary gonadotrope secretory organelles during the reproductive cycle, in ovariectomized animals and during a period of recovery from hyperprolactinemia. (5) Control of Muscle Protein Metabolism During Exercise. This project requires the proposed instrument in studying the role of lysosomes in muscle and liver damage resulting from prolonged strenuous exercise. The ultrastructure will be correlated with biochemical changes. Currently, these projects are being performed on two electron microscopes, one of which of which is experiencing a large amount of down time and a heavy user load. The other microscope is primarily dedicated to clinical diagnostics and is increasingly restricted for basic research. The acquisition of the proposed Zeiss EM10 Electron Microscope will not only assure the completion of the projects described above, but will benefit the entire user community by reducing the user load on the existing scopes. Furthermore, the proposed instrument possesses a goniometer stage which many of the major users and the research community are finding useful in discerning intracellular structures and organelles.